Control systems for storage and retrieval machines are subject to environmental problems such as electrical noise from other nearby electrically operated equipment, mechanical vibration of the storage and retrieval machine as it operates, and stress on wires due to substantially continuous operating movement with frequent starts and stops of the storage and retrieval machine. The continuous operating movement of the storage and retrieval machine also makes troubleshooting of the machine's control system while running particularly difficult. Storage and retrieval machine control systems also typically have extensive wiring requirements, relays with movable parts which wear over time, and control programs which are difficult to change.
The drives for most storage and retrieval machines are of A.C. wound rotor motor types using eddy current brakes and reactors or D.C. motors employing resistors and contactors to control armature voltage and thereby motor speed. These types of drives have low performance and efficiency, and poor control feedback systems.
As a result of the difficult environment in which control systems for storage and retrieval machines operate, design deficiencies of the control systems, and storage and retrieval machine drives which are difficult to control, storage and retrieval machines are relatively inaccurate in their operation, slow, and have an undesirably high level of safety problems.